Diagenesis of the Temperate Carbonate Unit of the Granada Basin (SE Spain) - Influence of the Tortonian Evaporites

The present work focuses on the study of the diagenetic evolution of carbonates rocks in contact with evaporites. Brine circulations are often associated with diagenetic modifications (ore deposition, dissolution, fluid escapes, etc.). The study of the mineralogical transformations occurring in sediments in contact with evaporites contributes to identify geochemical tracers of these fluid flows and to understand how rocks are mineralogically and petrophysically transformed by basin-scale brine circulation. To this study, the Tortonian Temperate Carbonate Unit deposited in the Granada sedimentary basin (SE Spain) was investigated. Before the deposition of the Tortonian evaporites, the Temperate Carbonate Unit underwent a marine calcite cementation and then a strong dissolution phase due to fresh-water percolation. The carbonates were subsequently shallow-buried and were stabilized and cemented by a low-magnesium calcite cement after mechanical compaction. During the deposition of the Tortonian Evaporites, the Temperate Carbonate Unit was probably sub-aerially exposed was firstly subject to pedogenesis and incorporated a Mg-smectite. During the Messinian, the carbonates underwent a second burial history during which strong saline conditions produced mainly dissolution of some terrigeneous grains and the dolomitisation of the initial micritic matrix and the Mg-smectite within a closed diagenetic system.